361 lines
13 KiB
C
361 lines
13 KiB
C
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// skipset.h -- set operations using a skiplist
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// Copyright (C) 2024 Mark Adler
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// See MiniZip_info.txt for the license.
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// This implements a skiplist set, i.e. just keys, no data, with ~O(log n) time
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// insert and search operations. The application defines the type of a key, and
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// provides a function to compare two keys.
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// This header is not definitions of functions found in another source file --
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// it creates the set functions, with the application's key type, right where
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// the #include is. Before this header is #included, these must be defined:
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//
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// 1. A macro or typedef for set_key_t, the type of a key.
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// 2. A macro or function set_cmp(a, b) to compare two keys. The return values
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// are < 0 for a < b, 0 for a == b, and > 0 for a > b.
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// 3. A macro or function set_drop(s, k) to release the key k's resources, if
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// any, when doing a set_end() or set_clear(). s is a pointer to the set
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// that key is in, for use with set_free() if desired.
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//
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// Example usage:
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//
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// typedef int set_key_t;
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// #define set_cmp(a, b) ((a) < (b) ? -1 : (a) == (b) ? 0 : 1)
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// #define set_drop(s, k)
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// #include "skipset.h"
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//
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// int test(void) { // return 0: good, 1: bad, -1: out of memory
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// set_t set;
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// if (setjmp(set.env))
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// return -1;
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// set_start(&set);
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// set_insert(&set, 2);
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// set_insert(&set, 1);
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// set_insert(&set, 7);
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// int bad = !set_found(&set, 2);
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// bad = bad || set_found(&set, 5);
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// set_end(&set);
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// return bad;
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// }
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//
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// Interface summary (see more details below):
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// - set_t is the type of the set being operated on (a set_t pointer is passed)
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// - set_start() initializes a new, empty set (initialize set.env first)
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// - set_insert() inserts a new key into the set, or not if it's already there
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// - set_found() determines whether or not a key is in the set
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// - set_end() ends the use of the set, freeing all memory
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// - set_clear() empties the set, equivalent to set_end() and then set_start()
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// - set_ok() checks if set appears to be usable, i.e. started and not ended
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//
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// Auxiliary functions available to the application:
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// - set_alloc() allocates memory with optional tracking (#define SET_TRACK)
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// - set_free() deallocates memory allocated by set_alloc()
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// - set_rand() returns 32 random bits (seeded by set_start())
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#ifndef SKIPSET_H
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#define SKIPSET_H
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#include <stdlib.h> // realloc(), free(), NULL, size_t
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#include <setjmp.h> // jmp_buf, longjmp()
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#include <errno.h> // ENOMEM
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#include <stdint.h> // int16_t, uint32_t, uint64_t
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#include <time.h> // time(), clock()
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#include <assert.h> // assert.h
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// Structures and functions below noted as "--private--" should not be used by
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// the application. set_t is partially private and partially public -- see the
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// comments there.
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// There is no POSIX random() in MSVC, and rand() is awful. For portability, we
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// cannot rely on a library function for random numbers. Instead we use the
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// fast and effective algorithm below, invented by Melissa O'Neill.
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// *Really* minimal PCG32 code / (c) 2014 M.E. O'Neill / www.pcg-random.org
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// Licensed under Apache License 2.0 (NO WARRANTY, etc. see website)
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// --private-- Random number generator state.
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typedef struct {
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uint64_t state; // 64-bit generator state
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uint64_t inc; // 63-bit sequence id
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} set_rand_t;
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// --private-- Initialize the state *gen using seed and seq. seed seeds the
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// advancing 64-bit state. seq is a sequence selection constant.
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void set_seed(set_rand_t *gen, uint64_t seed, uint64_t seq) {
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gen->inc = (seq << 1) | 1;
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gen->state = (seed + gen->inc) * 6364136223846793005ULL + gen->inc;
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}
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// Return 32 random bits, advancing the state *gen.
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uint32_t set_rand(set_rand_t *gen) {
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uint64_t state = gen->state;
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gen->state = state * 6364136223846793005ULL + gen->inc;
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uint32_t mix = (uint32_t)(((state >> 18) ^ state) >> 27);
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int rot = state >> 59;
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return (mix >> rot) | (mix << ((-rot) & 31));
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}
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// End of PCG32 code.
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// --private-- Linked-list node.
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typedef struct set_node_s set_node_t;
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struct set_node_s {
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set_key_t key; // the key (not used for head or path)
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int16_t size; // number of allocated pointers in right[]
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int16_t fill; // number of pointers in right[] filled in
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set_node_t **right; // pointer for each level, each to the right
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};
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// A set. The application sets env, may use gen with set_rand(), and may read
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// allocs and memory. The remaining variables are --private-- .
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typedef struct set_s {
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set_node_t *head; // skiplist head -- no key, just links
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set_node_t *path; // right[] is path to key from set_found()
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set_node_t *node; // node under construction, in case of longjmp()
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int16_t depth; // maximum depth of the skiplist
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uint64_t ran; // a precious trove of random bits
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set_rand_t gen; // random number generator state
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jmp_buf env; // setjmp() environment for allocation errors
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#ifdef SET_TRACK
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size_t allocs; // number of allocations
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size_t memory; // total amount of allocated memory (>= requests)
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#endif
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} set_t;
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// Memory allocation and deallocation. set_alloc(set, ptr, size) returns a
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// pointer to an allocation of size bytes if ptr is NULL, or the previous
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// allocation ptr resized to size bytes. set_alloc() will never return NULL.
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// set_free(set, ptr) frees an allocation created by set_alloc(). These may be
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// used by the application. e.g. if allocation tracking is desired.
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#ifdef SET_TRACK
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// Track the number of allocations and the total backing memory size.
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# if defined(_WIN32)
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# include <malloc.h>
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# define SET_ALLOC_SIZE(ptr) _msize(ptr)
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# elif defined(__MACH__)
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# include <malloc/malloc.h>
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# define SET_ALLOC_SIZE(ptr) malloc_size(ptr)
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# elif defined(__linux__)
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# include <malloc.h>
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# define SET_ALLOC_SIZE(ptr) malloc_usable_size(ptr)
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# elif defined(__FreeBSD__)
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# include <malloc_np.h>
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# define SET_ALLOC_SIZE(ptr) malloc_usable_size(ptr)
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# elif defined(__NetBSD__)
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# include <jemalloc/jemalloc.h>
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# define SET_ALLOC_SIZE(ptr) malloc_usable_size(ptr)
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# else // e.g. OpenBSD
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# define SET_ALLOC_SIZE(ptr) 0
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# endif
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// With tracking.
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void *set_alloc(set_t *set, void *ptr, size_t size) {
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size_t had = ptr == NULL ? 0 : SET_ALLOC_SIZE(ptr);
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void *mem = realloc(ptr, size);
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if (mem == NULL)
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longjmp(set->env, ENOMEM);
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set->allocs += ptr == NULL;
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set->memory += SET_ALLOC_SIZE(mem) - had;
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return mem;
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}
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void set_free(set_t *set, void *ptr) {
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if (ptr != NULL) {
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set->allocs--;
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set->memory -= SET_ALLOC_SIZE(ptr);
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free(ptr);
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}
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}
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#else
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// Without tracking.
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void *set_alloc(set_t *set, void *ptr, size_t size) {
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void *mem = realloc(ptr, size);
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if (mem == NULL)
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longjmp(set->env, ENOMEM);
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return mem;
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}
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void set_free(set_t *set, void *ptr) {
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(void)set;
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free(ptr);
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}
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#endif
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// --private-- Grow node's array right[] as needed to be able to hold at least
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// want links. If fill is true, assure that the first want links are filled in,
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// setting them to set->head if not previously filled in. Otherwise it is
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// assumed that the first want links are about to be filled in.
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void set_grow(set_t *set, set_node_t *node, int want, int fill) {
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if (node->size < want) {
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int more = node->size ? node->size : 1;
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while (more < want)
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more <<= 1;
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node->right = set_alloc(set, node->right, more * sizeof(set_node_t *));
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node->size = (int16_t)more;
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}
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int i;
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if (fill)
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for (i = node->fill; i < want; i++)
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node->right[i] = set->head;
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node->fill = (int16_t)want;
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}
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// --private-- Return a new node. key is left uninitialized.
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set_node_t *set_node(set_t *set) {
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set_node_t *node = set_alloc(set, NULL, sizeof(set_node_t));
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node->size = 0;
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node->fill = 0;
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node->right = NULL;
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return node;
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}
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// --private-- Free the list linked from head, along with the keys.
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void set_sweep(set_t *set) {
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set_node_t *step = set->head->right[0];
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while (step != set->head) {
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set_node_t *next = step->right[0]; // save link to next node
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set_drop(set, step->key);
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set_free(set, step->right);
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set_free(set, step);
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step = next;
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}
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}
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// Initialize a new set. set->env must be initialized using setjmp() before
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// set_start() is called. A longjmp(set->env, ENOMEM) will be used to handle a
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// memory allocation failure during any of the operations. (See setjmp.h and
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// errno.h.) The set can still be used if this happens, assuming that it didn't
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// happen during set_start(). Whether set_start() completed or not, set_end()
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// can be used to free the set's memory after a longjmp().
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void set_start(set_t *set) {
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#ifdef SET_TRACK
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set->allocs = 0;
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set->memory = 0;
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#endif
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set->head = set->path = set->node = NULL; // in case set_node() fails
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set->path = set_node(set);
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set->head = set_node(set);
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set_grow(set, set->head, 1, 1); // one link back to head for an empty set
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*(unsigned char *)&set->head->key = 137; // set id
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set->depth = 0;
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set_seed(&set->gen, ((uint64_t)(uintptr_t)set << 32) ^
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((uint64_t)time(NULL) << 12) ^ clock(), 0);
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set->ran = 1;
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}
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// Return true if *set appears to be in a usable state. If *set has been zeroed
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// out, then set_ok(set) will be false and set_end(set) will be safe.
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int set_ok(set_t *set) {
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return set->head != NULL &&
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set->head->right != NULL &&
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*(unsigned char *)&set->head->key == 137;
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}
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// Empty the set. This frees the memory used for the previous set contents.
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// After set_clear(), *set is ready for use, as if after a set_start().
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void set_clear(set_t *set) {
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assert(set_ok(set) && "improper use");
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// Free all the keys and their nodes.
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set_sweep(set);
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// Leave the head and path allocations as is. Clear their contents, with
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// head pointing to itself and setting depth to zero, for an empty set.
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set->head->right[0] = set->head;
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set->head->fill = 1;
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set->path->fill = 0;
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set->depth = 0;
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}
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// Done using the set -- free all allocations. The only operation on *set
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// permitted after this is set_start(). Though another set_end() would do no
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// harm. This can be done at any time after a set_start(), or after a longjmp()
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// on any allocation failure, including during a set_start().
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void set_end(set_t *set) {
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if (set->head != NULL) {
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// Empty the set and free the head node.
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if (set->head->right != NULL) {
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set_sweep(set);
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set_free(set, set->head->right);
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}
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set_free(set, set->head);
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set->head = NULL;
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}
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if (set->path != NULL) {
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// Free the path work area.
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set_free(set, set->path->right);
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set_free(set, set->path);
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set->path = NULL;
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}
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if (set->node != NULL) {
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// Free the node that was under construction when longjmp() hit.
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set_drop(set, set->node->key);
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set_free(set, set->node->right);
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set_free(set, set->node);
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set->node = NULL;
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}
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}
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// Look for key. Return 1 if found or 0 if not. This also puts the path to get
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// there in set->path, for use by set_insert().
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int set_found(set_t *set, set_key_t key) {
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assert(set_ok(set) && "improper use");
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// Start at depth and work down and right as determined by key comparisons.
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set_node_t *head = set->head, *here = head;
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int i = set->depth;
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set_grow(set, set->path, i + 1, 0);
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do {
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while (here->right[i] != head &&
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set_cmp(here->right[i]->key, key) < 0)
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here = here->right[i];
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set->path->right[i] = here;
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} while (i--);
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// See if the key matches.
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here = here->right[0];
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return here != head && set_cmp(here->key, key) == 0;
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}
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// Insert the key key. Return 0 on success, or 1 if key is already in the set.
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int set_insert(set_t *set, set_key_t key) {
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assert(set_ok(set) && "improper use");
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if (set_found(set, key))
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// That key is already in the set.
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return 1;
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// Randomly generate a new level-- level 0 with probability 1/2, 1 with
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// probability 1/4, 2 with probability 1/8, etc.
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int level = 0;
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for (;;) {
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if (set->ran == 1)
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// Ran out. Get another 32 random bits.
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set->ran = set_rand(&set->gen) | (1ULL << 32);
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int bit = set->ran & 1;
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set->ran >>= 1;
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if (bit)
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break;
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assert(level < 32767 &&
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"Overhead, without any fuss, the stars were going out.");
|
||
|
|
level++;
|
||
|
|
}
|
||
|
|
if (level > set->depth) {
|
||
|
|
// The maximum depth is now deeper. Update the structures.
|
||
|
|
set_grow(set, set->path, level + 1, 1);
|
||
|
|
set_grow(set, set->head, level + 1, 1);
|
||
|
|
set->depth = (int16_t)level;
|
||
|
|
}
|
||
|
|
|
||
|
|
// Make a new node for the provided key, and insert it in the lists up to
|
||
|
|
// and including level.
|
||
|
|
set->node = set_node(set);
|
||
|
|
set->node->key = key;
|
||
|
|
set_grow(set, set->node, level + 1, 0);
|
||
|
|
int i;
|
||
|
|
for (i = 0; i <= level; i++) {
|
||
|
|
set->node->right[i] = set->path->right[i]->right[i];
|
||
|
|
set->path->right[i]->right[i] = set->node;
|
||
|
|
}
|
||
|
|
set->node = NULL;
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
#else
|
||
|
|
#error ** another skiplist set already created here
|
||
|
|
// Would need to implement a prefix in order to support multiple sets.
|
||
|
|
#endif
|